Hydraulically operated wellbore liquid lift using casing gas as energy source

ABSTRACT

A system for lifting liquid from a wellbore includes a turbine selectively coupled to a source of gas flow originating in the wellbore. The turbine is arranged to convert the gas flow directly into rotation of the turbine. An hydraulic pump is rotationally coupled to the turbine. An hydraulic cylinder and piston are arranged to move a sucker rod string disposed in the wellbore. Control valves are provided to selectively apply gas flow to the turbine and hydraulic pressure from the pump to lift the piston and enable lowering thereof by the weight of the sucker rod string. The system further comprises control circuits configured to operate the control valves.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

The invention relates generally to the field of removal of liquid fromgas producing subsurface wellbores. More particularly, the inventionrelates to energy sources to operate hydraulic cylinder liquid liftingdevices for removal of liquid from such wellbores.

The oil and gas industry has undergone rapid development in the numberof wells drilled for natural gas production from “shale” reservoirs. Thenumber of such gas producing wellbores has increased the need forimproved means for deliquification (removal of water) of these wellswith typical liquid production rates and depths to as much as 12,000(can we do 14,000 ft??) feet.

Hydraulically operated vertical lift cylinders attached to the“wellhead” (control valves and related components at the surface tocontrol fluid flow into and out of the wellbore), like that ofelectrically or gas engine powered “pump jacks” (reciprocating beamoperated sucker rod pumps), provide advantage in many situations due tothe incremental stroking of the plunger pump to cause liquids to risemore steadily in a production tubing disposed within the wellbore“casing” (a protective pipe extending to proximate the bottom of thewellbore and typically cemented in place). The action of hydraulic liftcylinders for rod pump well deliquification overcomes a disadvantagecommon to plunger lift apparatus which tends to release a larger burstof liquid when moved upwardly in the well bore and with such liquidvolume comes associated gas. Such large volumes of liquid and gasreleased in a short time may cause the need for larger separationequipment, and sufficiently large surges of liquid and gas may disturbgas compressor operation.

Large surges of gas negatively affect compressor intake conditions,control and performance, whereas it can be appreciated that much moreattractive and steady flows of both natural gas and liquids are enabledusing hydraulic lift cylinder deliquification apparatus.

It is known in the art to use internal combustion (IC) engines to use aportion of the natural gas being produced from a wellbore to power aconventional beam pump jack. However, this method of producing the wellhas come under increasing regulatory scrutiny, and more stringentrequirements for a well operator to use costly emissions certified ICengines, purchase and maintain IC engine exhaust gas treatmentequipment, and costly time-consuming application for and maintenance ofair emissions permits has made such wellbore deliquification techniquesless attractive economically. In some geographic areas, for exampleCalifornia and the Texas Houston air quality attainment district,increased regulatory scrutiny and likely additional burdens will beplaced on oil and gas well operators within a relatively largegeographic areas.

Gas and oil wells tend to decline in production over time, and some evenincrease liquid (particularly water) production relative to natural gas,natural gas condensate and crude oil, the commonly valued constituentsof producing the petroleum well.

The industry's commonly accepted threshold limit for producing naturalgas and oil wells with the plunger lift method is described, forexample, in E. Beauregard, et al., Introduction to Plunger Lift:Applications, Advantages and Limitations, Presented at The SouthwesternPetroleum Short Course, Department Of Petroleum Engineering, Texas TechUniversity, Lubbock, Tex., Apr. 23-24, 1981. As can be appreciated, whenthe plunger lift method of production will no longer suffice, the oiland gas well operator has previously been faced with having to provideelectricity or burn a portion of his produced hydrocarbons in an ICengine to provide the power to operate a sucker rod pump to lift theliquids from the wellbore.

There exists a need for wellbore deliquification devices that do notrequire the use of external power sources, such as electricity and/or ICengines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example installation of a deliqufication apparatus.

FIG. 2 shows example hydraulic control circuits for the system of FIG.1.

FIG. 3 shows a modified form of the example shown in FIG. 2.

DETAILED DESCRIPTION

The present invention provides a device and method to be able to producehydrocarbons from wellbores previously unable to be produced as a resultof excessive liquid production in cases where electricity is unavailableor costly to install to the site. Although electricity installation towellsite would alleviate the air emissions burden, many wells arelocated either far from electricity access or where grid electricityaccess is difficult and costly. Since many wells have declined below theability to naturally flow as a normal progression in mature productiondecline, large numbers of wells exist where no grid electricityconnection has been provided to the wellsite and the costs of installingit are a substantial burden to profitable production of the well.

The present invention may also provide wellbore operators with theability to operate a sucker rod pump to remove liquid from wells tomaintain and in many cases increase production, with no burning of aportion of produced natural gas, nor any costly, time-consumingrequirement to seek regulatory approval for air emissions permit for ICengines, and thereafter the cost and maintenance associated withoperating the IC engine to the U.S. Environmental Protection Agency andany state regulatory air emissions standards.

FIG. 1 shows an example wellbore liquid lift installed on a wellbore.The wellbore terminates at the surface at the upper end of a wellborecasing 22. A casing head 22A may be used to seat therein a tubing hangerand production tubing (neither shown in FIG. 1 for clarity), wherein theproduction tubing is disposed inside the casing 22. The casing 22 mayinclude a discharge port and associated control valve, shown at 14, forventing natural gas pressure that accumulates in annular space betweenthe tubing (not shown) and the wellbore casing 22. Some of the ventedgas may be transferred through a line 19 to processing equipment (notshown in FIG. 1) to separate water to disposal, hydrocarbon liquids forsale and natural gas for eventual compression and transmission to a gastransmission pipeline (not shown).

Flow and pressure of the gas from the casing 22 may be controlled usinga control/regulation valve 16. The pressure and flow regulated gas maybe transferred through a hose or piping 17 to a power conversion unit12. The power conversion unit 12 uses flow of natural gas from thewellhead connection (discharge port 14) to operate a turbine (30 in FIG.2), the rotation of which may be used to operate an hydraulic pump (32in FIG. 2). The foregoing components will be further explained withreference to FIG. 2. The power conversion unit 12 may include controlcircuitry 12B including, for example, a microcontroller (not shownseparately) to operate the gas control valve 16, and/or hydraulic valvesas will be further explained with reference to FIG. 2. Electrical powerfor the power conversion unit circuitry 12B may be provided by batteriesand/or solar panels 12A.

Hydraulic power provided by the power conversion unit 12 may be used tooperate an hydraulic lift cylinder 20. The lift cylinder 20 may beconnected to the uppermost portion of the casing 22 with a wellheadconnection having an hydraulic oil port, shown generally at 13. Thehydraulic lift cylinder 20 may raise and lower a sucker rod string 20A.The sucker rod string 20A may be coupled at its lower end to aconventional wellbore fluid lift pump, including, for example, astanding valve and traveling valve therein (not shown in the figures).During operation, the power conversion unit 12 provides hydraulicpressure to cause the hydraulic cylinder 20 to lift the sucker rodstring 20A. When the sucker rod string 20A reaches a predetermined uppertravel limit, a switch 20B may operate to send a signal to the controlcircuitry 12B to allow controlled dropping of the sucker rod string 20Awithin the hydraulic cylinder 20 by release of hydraulic pressuretherefrom.

In other examples (not shown) where desirable, the cylinder 20 couldalso be mounted at lower portion on a pedestal spaced above the wellheadand coupled to the top of a conventional polished rod; the cylinder/rodcoupling would remain above a conventional stuffing box throughout itsstroke. An adjustable setting spring over ball backpressure valve isshown at 15. Such valves are commonly used to hold a backpressure oneither the tubing outlet or the casing outlet 14. Such valve 15 may beused in the present configuration to direct all flow of gas from thecasing outlet 14 to the turbine (30 in FIG. 2) up to a certain pressure,for example 100 to 150 pounds per square inch. Pressure exceeding thesetpoint opens the valve 15 and it then releases the gas being producedby the well in excess of what the turbine needs to go downstream toprocessing, possible compression and to a pipeline as explained above.

FIG. 2 shows an example turbine powered hydraulic unit to operate thehydraulic cylinder and sucker rod shown in FIG. 1. A turbine 30 isdisposed in the flow of gas from the casing 22 as explained withreference to FIG. 1. The turbine 30 is rotated by the movement of thegas, and such rotation may be coupled to an hydraulic pump 32 whichdraws fluid such as hydraulic oil from a reservoir 34. When it isdesired to lift the sucker rod string 20A, the control circuitry (12B inFIG. 1) may open the control valve 16 to enable turbine rotation andconsequent pump 32 rotation, thus pressurizing hydraulic fluid to flowinto the hydraulic cylinder 20 to lift the sucker rod string 20A byapplying hydraulic pressure under a piston 20C connected to the rodstring 20A. When the rod string 20A reaches the upper limit of itstravel, the switch (20B in FIG. 1) may close and cause the circuitry (12in FIG. 1) to close the gas supply control valve 16. The flow of gasfrom wellhead casing annulus ceases, as does then turbine rotation andhydraulic pump rotation. A check valve 36 causes the flow of hydraulicoil from out of the cylinder 20 (caused by the weight of the rod string20A) to be directed through a controllable orifice valve 38, which maybe manually or otherwise set to enable the rod string 20A to drop at apractical, optimal descent rate according to the well pumpingconditions. In another example, both the controllable orifice valve 38and the gas supply valve 16 can be configured to be in signalcommunication with the control circuitry 12B so that the rate ofupstroke lift and downstroke drop of the sucker rod string 20A may becontrolled to optimum benefit, and the control circuitry 12B may beorganized to be in remote communication via any wired or wirelesscommunication technique known in the art.

Shown at 44 is a pilot operated and adjustable set point (46 being theset point adjustment knob) pressure relief valve. Turning the knob 46changes the spring pressure on the relief valve 44 to obtain a selectedrelief pressure. By addition of pilot components including an orifice 48and a pilot valve 42 , the relief valve 44 can also be used to open andlet the hydraulic oil return on the downstroke out of the hydrauliccylinder 20 through the relief valve 44 into a filter 50 and ultimatelyinto the supply reservoir 34. The hydraulic fluid flow is checked at thehydraulic pump 32 outlet (by valve 40) to prevent reverse rotation ofthe hydraulic pump 32. By further explanation, by re-directing theinternal pilot line located upstream of the check valve 40, the reliefvalve 44 opens by reduced pressure at the pilot. Hydraulic fluid thenreturns through the filter 50. The function occurs due to the positionof sourcing pilot pressure port holding the valve 44 closed, (inconjunction with internal pilot valve balance spring) for the durationof time the hydraulic pump 32 operates to lift the sucker rod 20A. Whenthe upstroke lift has been completed, and the control circuitry 12Bturns off the gas flow to the turbine 30, the pressure on the pump sideof the check valve 40 drops and the relief valve 44 opens, lettingreturning hydraulic oil out of the cylinder 20 and ultimately into thereservoir 34.

The upper portion of the hydraulic cylinder 20 located above the piston20C may be filled with hydraulic fluid. The flow of hydraulic fluid outof and into the upper portion may flow through a fluid conduit 20D influid communication with the reservoir 34. Such configuration may bepreferred to accomplish several beneficial functions. The first is toprovide for more stable hydraulic oil volume in the reservoir 34; thisalso facilitates minimal reservoir level change in the reservoir 34 fromthe upstroke to the downstroke. Another possible benefit is minimizingoutside air and moisture exchange through a reservoir breather 52.Further, cooling of the hydraulic oil is facilitated with the cylinder20 releasing heat from the oil contained therein to the outside air,since in many installations the sucker rod string 20A can remain in itsdownward most position and at rest a substantial portion of the time.Any seepage past piston 20C seals may also be returned to the reservoir34 because the hydraulic cylinder 20 is hydraulically closed at bothends. The cyclic influx and discharge of hydraulic fluid may clean andlubricate the piston/cylinder interface for longer service life.

FIG. 3 shows a modified form of the example shown in FIG. 2, with theaddition of an accumulator arrangement useful for purposes of energyconservation that may be particularly useful when the system is used indeeper wells. The function of the accumulator 60 is to offset, orbalance part or all of the sucker rod string lift load. The sucker rodstring 20A may be made, for example, from steel and may weighapproximately 1.5 lbs per foot; thus a 10,000 foot length sucker rodstring would weigh approximately 15,000 pounds. In such example a 4.00inch bore diameter cylinder with a 1.5 inch diameter piston rod coupledto the sucker rod string would require (15,000/10.8) 1389 pounds persquare inch pressure applied under the piston 20C in the hydrauliccylinder 20 to balance the weight of the sucker rod string 20A of thisexample. In practice, only a portion of the total hydraulic fluidpressure required to offset the full weight of the sucker rod string 20Awill be used. The particular portion may be chosen according to theparticular well conditions, thus to generally maintain a sucker rodstring positive weight bias, yet reduce casing head gas and energyconsumption by almost half. A piston type accumulator may be preferred,with additional accumulator pressure bottles provided as needed, but theaccumulator 60 can also be of the bladder type, where a gas exerts forceon hydraulic fluid through a flexible barrier or membrane. The pump 32receives this hydraulic fluid under pressure to its suction port fromthe accumulator 60, reducing the energy required to be exerted by thepump 32 to lift the sucker rod string 20A. A filter 64 may be used toremove contamination from the hydraulic fluid and may be configured in amanner to prevent contaminants collected therein from being re-entrainedwhen the hydraulic fluid direction through the filter 64 is reversed.Upon completion of sucker rod lift, the relief valve 44 opens to returnthe hydraulic fluid under pressure to the accumulator 60, preservingenergy for the next sucker rod lift cycle. Pump shaft seal and/or pumpcase drain hydraulic fluid seepage losses that may result from thepressure imparted by the accumulator 60, pump and cylinder circuit canbe directed to a vent to the reservoir 34 and may be re-introduced tothe pressurized hydraulic circuit by a charge pump 62 through a checkvalve 63. An adjustable relief valve 61 may mediate the reintroductionof hydraulic fluid according to the relationship of its pressure settingto the lowest point of pressure exerted by the accumulator 60 on thepump 32 intake when the cylinder 20 has lifted the sucker rod 20A to itshighest position. The adjustable relief valve 61 also acts to protectthe charging circuit from over-pressure conditions.

While the example embodiments explained above with reference to FIGS.1-3 show the hydraulic cylinder and piston being directly coupled to thesucker rod string, it will be appreciated by those skilled in the artthat the above described system could also be used in versions ofreciprocating beam pump units (pump jacks) that are operated byselective expansion and contraction of an hydraulic cylinder and pistoncombination. In still other examples, rotation of the turbine may beconverted by devices known in the art to cause reciprocating motion ofthe beam in such pump jacks, e.g., gearing and rotating pitman arms orcranks.

A system and method according to the various aspects of the inventionmay use flow of natural gas out of a wellbore converted directly intomechanical energy to operate a liquid lift pump in the wellbore withoutthe need for external sources of energy, such as electricity, or withoutthe need to consume the gas to release its chemical energy (e.g., byinternal combustion or catalytic conversion.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A system for lifting liquid from a wellbore, comprising: a turbineselectively coupled to a source of gas flow originating in the wellbore,the turbine arranged to convert the gas flow directly into rotation ofthe turbine; an hydraulic pump rotationally coupled to the turbine; anhydraulic cylinder and piston arranged to move a sucker rod stringdisposed in the wellbore; control valves to selectively apply gas flowto the turbine and hydraulic pressure from the pump to lift the pistonand enable lowering thereof by the weight of the sucker rod string; andcontrol circuits configured to operate the control valves.
 2. The systemof claim 1 wherein the control valves comprise a gas supply controlvalve to cause turbine rotation when the sucker rod string requireslifting.
 3. The system of claim 1 wherein the control valves comprise acontrollable orifice valve in a line connecting the hydraulic cylinderto a reservoir, the controllable orifice valve arranged to enablelowering of the sucker rod string at a selected rate.
 4. The system ofclaim 1 further comprising an accumulator in hydraulic communicationwith an intake side of the hydraulic pump, the accumulator charged to aselected pressure and configured to recharge using hydraulic fluiddisplaced from the cylinder when the sucker rod string is allowed todrop.
 5. A method for lifting liquid from a wellbore, comprising:converting flow of gas from a wellbore directly into rotational energyusing a turbine disposed in the gas flow; converting the rotationalenergy into reciprocating motion; and using the reciprocating motion tooperate a sucker rod string disposed in the wellbore.
 6. The method ofclaim 5 wherein the converting rotational energy comprises rotating anhydraulic pump, and selectively directing pressure output from thehydraulic pump to an hydraulic cylinder/piston combination coupled tothe sucker rod string.
 7. The method of claim 6 further comprisingstopping rotation of the hydraulic pump, and selectively controllingrate of discharge of hydraulic fluid from the cylinder/pistoncombination to enable dropping the sucker rod string at a selected rate.8. The method of claim 6 further comprising prepressurizing the pumpwith pressure stored in an accumulator to at least partially offset aweight of the sucker rod string.
 9. The method of claim 5 wherein theflow of gas from the wellbore is from an annular space between awellbore casing and a wellbore tubing disposed within the wellborecasing.